Arc controlling electrodes for switches and gaps



Jan. 30, 1968 s. R. SMITH, JR 3,366,762

ARC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Filed April 16, 1965 3Sheets-Sheet 1 16 16' :f 0, 8 14 20 fiZl/en/fin 570%.? S'm'ifid; 3 yjMAT'M Jan. v30, 1968 s. R; SMITH, JR 3,366,752

ARC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Filed April 16, 1965 3-Shets-Sheet 2 b WPM MSW/51775;; I

Jan. 30, 1968 Y s. R. SMITH, JR

- A RC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Filed April 16, 19655 Sheets-Sheet 5 United States Patent 3,366,762 ARC CONTROLLINGELECTRODES FOR SWITCHES AND GAPS Sidney R. Smith, Jr., Stockbridge,Mass., assignor to General Electric Company, a corporation of New YorkFiled Apr. 16, 1965, Ser. No. 448,787 9 Claims. (Cl. 200-144) ABSTRACTOF THE DISCLOSURE A circuit interrupter or gap having a cup shapedcontact or electrode with a reentrant rim surrounding a second contactor electrode so as to produce an electromagnetic force on an arc betweenthe bottom of the cup shaped electrode and the end of the otherelectrode so as to confine the are within the cup shaped electrode.

This invention relates to electric arcs and more particularly to theirauto-confinement and control.

An example of where arc control is important is in vacuum switches, butthe invention is not limited to such switches and can be used inordinary switches or in gap devices such as are found in lightningarresters or in other electrical devices where confinement and controlof an electric arc is desirable. A reason why are control isparticularly important in vacuum switches is that because of thecomparatively high vacuum that must be maintained their volume, andhence size, should be as small as possible. On the other hand, highenergy arcs tend to spread and get out of control and vaporize theelectrodes carrying metal vapor onto the insulating walls of thehousing, inviting failure to interrupt. These factors, therefore, limitthe interrupting capacity of a given size vacuum switch of ordinaryconstruction. By preventing the are from spreading, the size of a vacuumswitch of given interrupting ability can be substantially reduced.

An object of the invention is to provide a new and improved means forconfining and controlling an electric arc.

Another object of the invention is to provide a novel electromagneticmeans for self-controlling and confining an electric are.

A further object of the invention is to provide a novel arcing electrodeconfiguration.

An additional object of the invention is to provide an improved electricswitch contact configuration.

An added object of the invention is to provide a new and improved vacuumswitch of increased interrupting ability per unit size.

In accomplishing the objects of the invention at least one cup shapedelectrode with a re-entrant lip portion cooperates with anotherelectrode for automatically confining by inherent electromagnetic actionan are between the electrodes to the space between the electrodes. Bymaking one of the electrodes a rod shaped contact and confining the arcto the interior of the cup shaped electrode as the other contact, thelatter will also function as a metal vapor shield in a vacuum switchthus making it possible to eliminate such a shield as a separate elementin vacuum switches.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings and its scope will bepointed out in the appended claims.

In the drawings,

3,366,762 Patented Jan. 30, 1968 FIG. 1 is a perspective view of avacuum switch employing the invention,

FIG. 2 is a longitudinal sectional view of the switch shown in FIG. 1taken on line 2-2 of FIG. 1,

FIGS. 3, 4, 5, 6, 7 and 8 are views similar to FIG. 2 of modifications,and

FIGS. 9 and 10 are respectively orthographic and isometric halfsectional views of another modification employing a pair of cup shapedelectrodes or contacts.

Referring now to the drawings, and more particularly to FIG. 1, there isshown therein a vacuum switch 1 comprising by way of example acylindrical housing 2 of suitable insulating material such as glass orceramic material provided with metallic end caps 3 which are sealed tothe ends of the housing 2 in any suitable manner so as to form a vacuumtight envelope or enclosure. Extending from the lower end of theenclosure is an electrical terminal connection 4 and extending from theupper end of the enclosure is an electrical terminal connection 5. Theterminal 4 is fixed and the terminal 5 is movable by means of a bellows6, the lower end of which is sealed to the upper end cap or plate 3 andthe upper end of which is sealed to a flange 7 on the terminal connector5.

The interior construction of the switch is shown in FIG. 2 and will beseen to consist of a cup shaped metallic or conducting electrode orcontact 8 from the center of whose bottom extends outwardly the terminalconnection 4. The portion of the terminal connection 5 which extendsinto the switch is a rod like conductive member 9 which extends into thecup electrode 8 and on the lower end of which adjacent the bottom of thecup shaped electrode 8 is an arcing electrode or contact portion 10shown as being dumbbell shaped in cross section but, of course, beingactually circular with indented central portions on both sides. Attachedto the rim of the cup 8 is a metallic or conductive re-entrant inwardlyextending lip portion 11 surrounding the rod 9 and extending inwardlytoward the bottom of the cup member 8. The switch can be closed bymoving the parts 5, 9, and 10 downwardly until part 10 contacts thebottom of the cup 8 or moving the parts 5, 9, and 10 upward until theupper edge of the part 10 engages the lower end of the inwardlyextending re-entrant lip portion 11. FIG. 2 shows the switch in its openposition where there is no contact between the parts 10 and the parts 8or 11.

The operation of FIG. 2 as thus far described is as follows. Assume thatthe switch attained its illustrated open position by raising the arcingcontact member 10 from the bottom of the cup 8. This will initially drawan are 12 which will be fed by current having a curved or kinked path inthat the current will flow generally horizontally through portions ofthe member 10 and the bottom of the cup 8 between the rod 9 and the are12 and between the are 12 and the terminal connection 4. As a result ofthis so-called current loop, the magnetic flux density on the inner sideof the loop corresponding to the right-hand side of the arc 12 as viewedin FIG. 2 will be greater than the flux density on the opposite side sothat an automatically produced electromagnetic force will tend to movethe arc to the left as viewed in FIG. 2, i.e., clockwise about the endof the electrode or contact 10 so that the arc will successively assumepositions 13, 14, 15 and 16. However, in the position 16 the arc will befed through the re-entrant lip portion 11 which extends in the oppositedirection from the Wall of the cup shaped member 8 so that theelectromagnetic force will reverse and the arc will be forced back tothe position 15. Then the original force which caused it to jump fromposition 15 to position 16 will again come into play so that the arcwill rapidly jump back and forth between positions 15 and 16.

Even if the arc were to over-shoot the position 16 to a position 17between the lip portion 11 and the rod 9, the electromagnetic forcewould be such as to drive the arc downward and back to position 15.

Essentially the same action would take place if the switch had come froman upward closed position where movable contact was touching the lowerend of the re-entrant lip portion 11 to the open position shown in FIG.2, except that in that case the arc would first be drawn at position 16and would then be forced to jump to position and back and forth betweenthose positions as already described.

The result is that the arc is confined within the cup shaped electrodeor contact 8 so that little or no contact metal vaporized by heat of thearc can escape from the cup but all such vaporized metal will simplycondense on the metallic surfaces within the cup. Consequently, theconventional metal shield which is normally interposed between thecontacts of a vacuum switch and its insulating envelope such as theinsulating cylinder 2 can be eliminated. The function of such a shieldis, of course, to condense vaporized metal and prevent it fromcondensing on and coating the surfaces of the insulating cylinder orenvelope so as to cause ultimate short circuiting or failure of theswitch. It also tends to avoid weakening of the ceramic by heat shock.

If desired, means may be provided for rotating the arc about the commonaxis of the cup 8 and rod 9. One such means can be a conductive coil 18for immersing the arc in a magnetic field which extends generallyparallel to the common axis of the cup 8 and rod 9, this coil beingconnected serially in the circuit. The interaction of the horizontalcomponent of the arc current and the vertical magnetic field will causea tangential force to be applied to the arc, thus rotating it orspinning it about the axis of the switch. This, of course, has thedesirable effect of keeping the electrodes from melting or burning awayat a particular point because it does not continuously play betwen fixedspots on the electrodes.

Ordinarily, in the case of alternating current, the arc will beextinguished at the first current zero.

If desired, the rod 9 can be provided with a shield 19 for condensingwhat small amount of vaporized metal may escape from between the rod 9and the lip 11.

Preferably, the radial distance between the rod 9 and the lip portion 11is smaller than the radial distance between the lip portion 11 and thewall of the cup member 8, and preferably the axial length of the lipportion 11 is a sizable fraction of the arc chamber height.

Referring now to the modification shown in FIG. 3, the principaldifferences are that the movable contact 10' is more disk shaped thanthe dumbbell shaped contact 10 of FIG. 2, and a circular cooperatingbead or raised portion is provided on the inner bottom surface of thecup shaped contact 8. This is to insure the formation of a current loopor kink which will, when the initial are 12 is formed, start it aroundto its ultimate alternate positions 15 and 16 as described in connectionwith FIG. 2. Another dilference is that in FIG. 3 the bellows 6 ismounted internally instead of externally and the shield 19 isconsequently somewhat frustoconical in shape.

Referring now to the modification shown in FIGS. 4 and 5, this isgenerally similar to FIG. 2 except for the shape of the parts forcausing arc motion. Thus while the movable contact 10" is generallysimilar in vertical cross section to the movable contact 10 of FIG. 3the central inner bottom surface of the cup shaped electrode or contact8 is dished at 21 so as to insure that an initial are drawn between thebottom of the cup 8 and the bottom of the contact 10" will be off axisso as to produce initially the required current loop or kink for movingthe arc to its ultimate alternate positions 15 and 16.

Also, instead of employing the separate coil 18 shown in FIG. 2 forcausing arc rotation, angularly or spirally extending slots 22 are cutin the movable contact 10 as shown by the sectional view illustrated inFIG. 5 which is a horizontal sectional view of the contact 10 taken online 5-5 of FIG. 4. By means of these slots 22, the current flowing inthe contact 1% is given a tangential component in addition to its normalradial component which it has in FIGS. 2 and 3. This tangentialcomponent of the current applies a tangential electromagnetic force tothe arc causing it to spin around the vertical axis of the switch in thesame way that the coil 18 of FIG. 2 causes it to spin.

If desired, this action may be supplemented or substituted for bycomplementary angularly or spirally extending slots 23 cut in there-entrant lip member 11 so that in the same way current flowing to orfrom the are through the vertical portion of the lip member 11 will havea tangential or circumferential component for causing the arc to spinabout the axis of the device. Of course, if both the movable contact 10"and the lip portion 11 are slotted, care must be taken that the slotsextend in complementary angular directions so that the are spinningforces produced thereby will be in the same direction. While angularlyor spirally slotting the outer walls of the cup shaped member 8 wouldtend to spin the arc in its transistory positions 12, 13 and 14, this ishardly necessary because the arc does not stay long enough in any one ofthese positions and actually it is undesirable because this wouldprovide openings in the outer walls of the cup 8 which would allowescape of vaporized contact metal which would then coat the innersurface of the insulating envelope 2 unless a separate vapor shield wereprovided.

It will, of course, be understood that the coil 18 of FIG. 2 or theslots 22 of FIG. 5 or the slots 23 of FIG. 4 can be used singly or incombination in all of the various species of the invention when it isdesired to cause the arc to rotate.

In the modification shown in FIG. 6, the rod 9 and/or the terminalconnection 4 are made of magnetic material to influence the magneticflux distribution near the contacts and to provide greater stiffness orelectromagnetic force for moving the arc and confining it between itsposition 15 and 16.

In the modification shown in FIG. 7, the insulating housing 2' is shownas of generally H-shaped cross section with a metal case 24 extendingaround the bottom half and sealed thereto and to the bottom of the cupshaped contact 8. The opening in the crossbar of the H being sealed bythe bellows 6 between which and the rod 9 there is a modified shapeshield 19" if desired. The movable contact 10' is also shown of somewhatdifferent shape, being hollow.

In the modification shown in FIG. 8 the re-entrant lip 11' fits over therim of the cup 8 and is comparatively short because in general thelength of the inwardly extending re-entrant lip is proportional to theinterrupting rating of the switch, and for switches of comparatively lowinterrupting rating such as the one illustrated in FIG. 8 the lip 11'can be shortened. Also the movable contact 10"" consists of a plain capfitted over the end of the rod 9 and a mating fixed contact 20' is a capfitted over the end of the terminal connection 4 at the bottom of thecup 8. While this construction does not show any means for insuring aninitial loop or kink in the current feeding an initial arc, arcsinherently have a characteristic of wandering so that even if theinitial arc were exactly on the axis of the device it would move enoughto create a small loop or kink which then would force it furthersidewise to produce the resulting action in the are as described inconnection with the previous figures particularly FIG. 2.

1n the modification shown in FIG. 9, there are two cup shaped electrodes25 and 26 with re-entrant inwardly extending lip portions 27 and 28,respectively. They are arranged in mouth facing mouth relation and whenspaced as illustrated constitute a gap so that current flowing between aterminal 29 for electrode 25 and a terminal 30 for an electrode 26 willjump the gap between them. However, they obviously may be the contactsof a switch in which case they will be relatively movable in theircoaxial direction so that when they are in contact the switch will beclosed and when they are separated the switch will be open. They can, ofcourse, be located in an evacuated envelope as in the preceding figuresso as to constitute a vacuum switch. It will be understood, of course,that FIG. 9 is an orthographic sectional view through the central axisand that actually the cups have re-entrant surfaces extending all arounda common axis as shown by the isometric sectional view in FIG. 10.Consequently when they are separated as shown in FIG. 9 they constitutea special type of horn gap having a lateral dimension which is actuallya closed re-entrant surface, this being a surface of revolution if thecups are circular in horizontal cross section. The re-entrant portions27 and 28 are preferably provided with c0rnple mentary sloping angularor spiral cuts or slots 31 and 32 respectively for the purpose ofspinning an are around the common longitudinal axis which, of course, isa central vertical axis as viewed in the drawing. The direction ofrotation is as indicated by the arrowed circle at the bottom of FIG. 10.

The operation of FIG. 9 is as follows. Assume an are 33 is drawn orstruck between the electrodes 25 and 2-6. This is at a point of minimumspacing and it will be seen that current flowing into and out of thatarc between the terminals 29 and 30 along the sides of the cups 25 and26 will have a loop or kink thus forcing the arc inward toward thecenter or common axis so that the arc will rapidly progressively assumethe dashed line positions 34, 35, 36 and 37. This same action would takeplace regardless of where on the perimeters of the mouths of the cups 25and 26 the are 33 initially for-ms. At the same time the arc is causedto move along this perimeter or, in other words, rotate about the commonaxis because the skewed teeth or cuts 31 and 32 produce tangentialcomponents in the direction of current flowing into and out of the arc.These tangential components have the same direction because the anglesof skewing of the cuts or teeth are such as to take account of thedirections of the current when it enters and when it leaves the arc.

Of course, the higher the arc current, the greater the electromagneticforce tending to force the arc inward toward the center and also thegreater the force tending to spin it about the axis. In this manner, thearc is automatically and practically instantaneously driven inward,elongated, and cooled by the horn gap action supplemented by thespinning action so that the arc can go completely around the electrodeaxis many times in a half cycle of 60 cycle current.

To facilitate manufacture it is preferable to make the upper and lowerhalves of FIG. 9 exact duplicates as shown but this, of course, is notnecessary.

The vacuum switches can, of course, be evacuated in any suitable mannersuch as by pumps of either the mechanical or the diffusion type or bothin series or in a pumpless manner according to the method disclosed andclaimed in De Santis et a1. United States Patent 2,934,392 which isassigned to the present assignee.

It will, of course, be understood that the previously used termshorizontal and vertical refer only to the drawings when they are placedin an upright position and that actually the invention in nowise dependson any particular orientation of the devices in space.

While there have been shown and described particular embodiments of theinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention, andtherefore it is intended by the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope ofthe invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, an arc confining electrode structure including a pairof spaced electrodes between which an arc is drawn, one of saidelectrodes being cup shaped, the other being rod shaped and extendinginto said cup shaped electrode through the mouth thereof to the bottomthereof, the rim of said cup shaped electrode having a reentrant lipportion extending inwardly toward the bottom thereof around said rodshaped electrode, said cup shaped electrode and re-entrant lip portionforming current paths of loop shape such that electromagnetic forcesproduced by current flow through the bottom of the cup shaped electrodeand through the re-entrant lip portion retain all arcs within theconfines of the cup shaped electrode.

2. The combination of claim 1 provided with means for rotating an arcbetween said electrodes about the axis of said cup and rod.

3. A combination as in claim 2 in which said means is a series of spiralcuts in at least one of said electrodes.

4. An arcing duty electric switch comprising, in combination, a cupshaped contact having a terminal extending outwardly from the center ofthe bottom thereof, a second contact in said cup shaped contact forengaging the bottom surface thereof, said second contact being mountedon the end of a conductive rod extending axially of the cup shapedcontact out of the mouth thereof and being movable in said axialdirection, the rim of said cup shaped contact having a re-entrantportion extending inwardly toward the bottom thereof, whereby currentflow between said terminal and the outer end of said rod which feeds anare between said contacts will have current paths of loop shape whichproduce electromagnetic forces which in the case of an arc to saidre-entrant portion drives said are into said cup shaped contact and inthe case of an arc to the wall of said cup shaped contact drives saidare in the opposite direction toward said re-entrant portion.

5. In a vacuum circuit interrupter, a circular cross section cup shapedcontact having a terminal extending outwardly from the center of thebottom thereof, a circular cross section second contact in said cupshaped contact for engaging the bottom thereof, said second contactbeing mounted symmetrically on the end of a smaller diameter rodextending axially of said cup shaped contact out of the mouth thereof,the rim of said cup shaped contact having a re-entrant lip portionextending inwardly toward the bottom thereof, said rod being axiallymovable whereby an arc drawn between said contacts when they separate isdriven by electromagnetic force along the Wall of the cup shaped contacttoward said re-entrant lip portion but an arc to said re-entrant lipportion is driven in the opposite direction back to the wall of said cupshaped contact.

6. In a vacuum circuit interrupter, a circular cross section cup shapedcontact, a circular cross section disk contact in said cup shapedcontact for engaging the bottom thereof, said disk shaped contact beingmounted symmetrically on the end of a rod of smaller diameter extendingaxially of said cup shaped contact out of the mouth thereof, the rim ofsaid cup shaped contact having a reentrant lip portion extendinginwardly toward the bottom thereof.

7. In a vacuum circuit interrupter, a circular cross section cup shapedfixed contact having an external terminal extending axially outward fromthe bottom thereof, a circular cross section movable disk contact forengaging flatwise between its center and its rim the inner bottomsurface of said cup shaped fixed contact, a straight conductiveactuating rod terminal for said movable disk con tact of smaller crosssection than said disk contact connected to the center thereof andextending axially of said 3,366,762 7 8 cup shaped contact out of themouth thereof, the rim of References Cited said cup shaped contacthaving a re-entrant lip portion UNITED STATES PATENTS extending inwardlytoward the bottom thereof for confining withtin said cup shaped contactby electromagnetic 9 9 1935 efi action an are 'between the rim of saiddisk contact and the 5 3,014,108 12/ 1961 Cobi t 1, 200-144 innersurface of said cup shaped contact. 6 h 3 014 109 12/1961 Burger 2O0 1448. A circuit interrupter as in c aim provide-d wit means for rotating anare between said contacts about the 3185797 5/1965 Pqter 200-144 axis ofaid cup and rod TIUJS 9. A circuit interrupter as in claim 8 in whichsaid 10 3,261,954 7/ 1966 Yonkers 200-144 means is a series of spiralcuts in at least one of said contacts. ROBERT S. MACON, PrimaryExaminer.

